We have achieved significant enhancement of gene delivery into livers of large animals using ultrasound (US)-targeted microbubble (MB) destruction methods. An infusion of pGL4 (encoding a luciferase reporter gene) plasmid DNA (pDNA) and MBs into a portal-vein segmental branch of a porcine liver was exposed to US for 4 min. Therapeutic US induced cavitation of MBs to temporarily permeabilize the vascular endothelium and cell membranes, allowing entry of pDNA. We obtained a 64-fold enhancement in luciferase expression in pig livers compared to control without US using an unfocused, dual-element transducer (H105, center frequency [fc] = 1.10 MHz) at 2.7 MPa peak negative pressure (PNP). However, input electrical energy was limited, and modified transducers were designed to have spherical (H185A, fc = 1.10 MHz) or cylindrical foci (H185B, fc = 1.10 MHz; H185D, fc = 1.05 MHz) to enhance PNP output. The revised transducers required less electrical input to achieve 2.7 MPa PNP compared to H105, thereby allowing PNP outputs of up to 6.2 MPa without surpassing the piezo-material limitations. Subsequently, luciferase expression significantly improved up to 9,000-fold compared to controls with minor liver damage. These advancements will allow us to modify our current protocols toward minimally invasive US gene therapy.
A commercially available catheter (EKOS EkoSonic catheter) has been used in the clinic with lytic drugs to clear blood clots associated with pulmonary embolism, deep vein thrombosis and peripheral arterial occlusion. Operating at 2.3 MHz, transducers within the catheter deliver short, variable amplitude pulses at intensities between 3.4 and 11.5 W/cm2. Lysis enhancement in the presence of ultrasound is non-thermal and generally attributed to increased transport and, therefore, increased efficiency of the lytic. The enhanced lytic effect may also be associated with increased availability of lytic binding sites associated with changes in the clot’s fibrin structure. To better understand the specific effects of ultrasound on fibrin networks within blood clots, we utilized scanning electron microscopy (SEM) and clot turbidity measurements to observe and quantify changes in fibrin mesh. SEM images of Factor XIII-depleted fibrinogen clots show a significant decrease (p < 0.05) in fibrin fiber diameter in the presence of ultrasound (33.8 ± 17.2 nm) compared to control (63.4 ± 24.0 nm). Clot turbidity is reduced following treatment with ultrasound, which correlates with decreased fiber diameter. These results indicate that ultrasound alters fibrin structure, which may contribute to enhanced binding of lytic drug and clot lysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.